Manufacture of soap



atented June 35, 1943 UNETED STATES ?AT direct and mesne assignments, toThe Sharples Corporation, Philadelphia, has a corporation of Delaware NoDrawing. Application April 23, 1941, :Serial No. 389,888

(c1. zen-412.5)

19 Claims.

The present invention pertains to the manufacture of soap, and is morparticularly concemed with the purification of the product known asnigre, obtained in the soap-making process.

In accordance with the conventional procedure for making soap by thefull boiled" or settled process, an oil or fat is initially boiled witha quantity of caustic. soda solution which is somewhat lessthan theamount which would theoretically be required for completesaponification. When the alkali has been substantially completelyutilized in converting the fat into soap, the soap .formed by reactionof the caustic soda with the fat, and unsaponified oil or fat, aregrained out or salted outby the addition of concentrated brine or drysalt. The action of the brine is to cause the soap to precipitate in theform of soap curds, and these curds rise to the top of the soap kettle.This permits withdrawal from the bottom of the kettle f the "spent lye,which is the water solution of salt, glycerine, and any slight excess ofalkali which may be present, together with some impurities and coloringmatter. This spent lye is subjected to special treatment for glycerinerecovery.

The soap curd remaining in th kettle at the end of these operations istreated with a further quantity of caustic soda solution to complete thesaponification of any neutral fat which may not have been saponified inthe previous treatment. After saponification is completed by boiling theresulting mixture, the soap is again grained by addition of salt or afurther quantity of caustic soda solution, and the soap curds are againseparated from the resulting aqueous After completion of saponiiicaticnof the fat by a series of saponification steps such as discussed above,called changes, and washing the product in one or more additionalchanges with a brine solution, there is obtained a soap-containing masswhich contains grained soap, water, free alkali (unneutralized sodiumhydroxide), salt, and miscellaneous foreign matter including anundesirable quantity of dirt and other-undesired impurities. It isnecessary that the quantity of free alkali, salt and foreign matter inthe soap-containing mass be materially reduced in order to obtain anacceptable grade of soap, regardless of whether this soap is to be usedas a toilet soap or a laundry soap. In order to attain this result, thesoap-maker subjects this mass to a fitting or finishing operation.

much smaller proportion of salt, free alkali and dirt than thesoap-containing mass from which it is produced. This neat soap issubjected to further treatment, which varies in accordance with the typeof soap being produced, in manufacturing the desired commercial product,but these steps do not concern us in the present discussion.

The free alkali, salt and foreign impurities from the originalsaponified product are, for the most part, retained in the lowerstratified layer, or nigre. These impurities are present in the nigre toan objectionable extent, and this material cannot therefore be directlyutilized in producing the familiar soaps of commerce. Re gardless ofwhether the nigre or equivalent substance is produced by the above orsome other sequence of steps, it contains a very large proportion ofsoap, and any soap-making process which failed to utilize the soapvalues of the nigre would, therefore, be highly uneconomical.

In conventional soap-making procedure, the nigre is mixed with a furtherquantity of fat and lye in the manufacture of a further batch of soap,and is treated along with this further quantity of fat and lye, in oneof the earlier saponi-' fication steps discussed above. By operating inthis fashion, the'soap contained in the nigre becomes a part of the nextbatch of soap, and is, for the most part, retained in the neat soap ofthe succeeding batch, upon the performance of the fitting step on thatbatch. The utilization of the nigre in this manner has the disadvantage,

The fitting operation is accomplished by add= however, that it resultsin the degrading of the next batch of soap by addition to theingredients of that batch of the least desirable constituents of thepreceding batch. In the interests of economy, the nigre is recycled to asucceeding soapmaking batch as long as this may be continued withoutimpairing the quality of the soap derived from the succeeding batches totoo great an extent. It is self-evident from the above discussion,however, that the amount of impurities in the nigre as well as in theresulting neat soap increases progressively as the recycling of thenigre is continued, and this recyclingoperation must, accordingly,ultimately be discontinued.

In conventional procedure, when the nigre becomes degraded to a point atwhich recycling in manufacture of a particular grade of soap isimpossible, the nigre, instead of being entirely discarded, is mixedwith fat and alkali entering into the making of an inferior grade ofsoap, and the recycling of the nigre in the manufacture of this inferiorgrade of soap is continued until the nigre becomes too poor to be usedfurther in this operation. While the exact sequence of steps ofrecycling the nigre and/or passing it to a saponification step inmanufacture of an inferior grade of soap varies considerably, dependingupon the, quality of soap to be produced and other considerations, theabove discussion covers the general principle of re-use of the nigre torecover the soap which it contains.

The above discussion afiords an approach to a statement of the nature ofthe present invention. A feature of the invention is the removal offoreign impurities from the nigre before recycling the nigre to thesucceeding soap-making batch, thereby avoiding progressive increase inthe amount of foreign impurities in successive batches of nigre, andpermitting continuation of the operation of recycling the nigre, withoutthe degradation which'has occurred in prior artpractice.

By the practice of the invention, the soapmaker is able to perform aneffective removal of impurities from the nigre. At the same time, he-isable to effect removal of impurities from the nigre-by a procedure whichinvolves utilization of materials whichordinarily enter the soap-makingprocess, thereby permitting all of the materials introduced for thepurpose of assisting in removal of impurities from the nigre to beutilized in the manufacture of coap.

Further advantages of the invention will be evident from the followingdiscussion, and the manner in which these advantages have been attainedwill also be evident from that discussion.

The present invention rests upon the discovery that it is possible toeffect removal of practically all of the undesired impurities fromthenigre provided material constituting a source of acid is first mixedwith the nigre and reacted with the alkali of the nigre to reduce thefree alkali content of the nigre. Thus, in the practice of theinvention, an acid or ester is mixed with the nigre, and the resultingmixture is preferably heated to a temperature sumciently high to effectfairly rapid reaction between the free alkali of the nigre and the acidor ester employed to reduce the free alkali concentration.

In the preferred practice of the invention, a high molecular organicacid or ester is added to the nigre for reaction with the free alkaliwhich is present. The resulting mixture is then heated to a temperaturewhich may be in the neighbor-- hood of the boiling point of water, inorder to cause reaction between the free alkali and source of acid toproduce soaps oi the acids or esters employed. when the quantity of freealkali has been substantially reduced or entirely eliminated byneutralization by the acid or ester, it will be found that most of theforeign impurities may be removed by appropriate treatment.

Among the preferred materials which may be used for neutralization ofthe free alkali of the nigre in the practice of the invention are thevarious fatty acids and fats, and other high molecular organic acids andesters thereof, such as the various oils and fatty acids whichordinarily enter into the soap-making operation. Thus, cocoanut oil,tallow, cottonseed oil, corn oil, palm kernel oil, soya bean oil, rosin,or any one of a large number of other organic esters or acids obtainedby splitting of such esters may be used in the practice of theinvention. We have obtained our best results by the use of cocoanut oilor cocoanut oil fatty acids in this connection, since the neutralizationof free alkali by cocoanut oil or cocoanut oil acids results inproduction of a mass from which undesired impuritreatment, such as theapplication of centrifugal force.

In the preferred practice of the invention, a suflicient amount of thematerial constituting the source of neutralizing acid is added to thenigre to eiiect substantially complete neutrali-' zation of thefreealkali, and even an exces the material constituting the sourcevofacid may be used, in order to assist in obtaining rapid and completereaction of the acid with the alkali present.

After a substantial proportion of the free alkali has been neutralizedby the operations discussed above, the resulting mixture is subjected toa separating operation which, in the preferred embodiment of theinvention, involves centrifugation. When the treated nigre is subjectedto high centrifugal force, practically all of the undesired impuritiesare removed, and the resulting purified mixture may then be recycleddirectly to the first or any subsequent saponification step of thesoap-making process, and subjected to further treatment together withthe alkali and fat employed in the subsequent soap-making operation.

The advantages obtained by the practice of the invention will now beapparent. In the first place, the neutralization of the free alkali byaddition of an acid has the effect, for reasons which we do not fullyunderstand, of making it possible to remove the dirt and other undesiredimpurities almost completely from the nigre. By reason of theaccomplishment of this result, it is possible to effect recycling of thenigre almost indefinitely to succeeding soap-making batches. and toeffect improvements both in the quality of the soap produced and in theeconomics of the soap-making process. But these results areaccomplished, in contradistinction to previously proposed methods ofpurifying the nigre, in a manner which introduces no additional expenseto the fundamental steps of the soap-making operation. By using, as theester or acid added to the nigre to reduce the quantity of free alkalipresent, a material which normally enters into the soap-makingoperation, we are able to effect removal of undesired impurities fromthe nigre without addingany expense whatever, for the same quantity ofester or acid would be utilized and the same heat required to effectreaction if the free alkali were neutralized by return of the mm to thesucceeding soap-making operation without first adding the fat or acid.Thus, when the ordinary soap-making fats or acids are used toprecondition the nigre for clarification, this preconditioning stepmerely involves effecting saponification of a part of the fat or acid tobe used in the ensuing soap-making operation at a slightly earlier stagethan would otherwise be the procedure.

Various modifications will be obvious to those skilled in the art.Instead of using, as a source of acid to neutralize the free alkali ofthe nine.

an ester or acid such as ordinarily used in soapmaking, other esters oracids capable of furnishing an acid radical for combination with thefree alkali may be employed. Thus, aliphatic and aromatic sulfonic acidssuch as have recently come into wide use as washing, wetting andemulsifying agents may be added to the nigre for reaction with the freealkali to furnish the appro-' priate salts of such acids, or a widevariety of other organic and inorganic acids and esters may ties may bereadily separated by appropriate be employed.

- in combination with the performance of the step of neutralizing thefree alkali with an acid, and that advantageous results are obtained insome cases by diluting with water the mixture of nigre and added acid.

Example I A mass of soap nigre was placed in a large kettle and heatedto 210 F. The nigre ,was thoroughly agitated during the heating period,

' and this agitation was continued during the feed of the nigre to acentrifugal separator at a rate of 1680 lbs. per hour. Prior tocentrifugation, the nigre contained 1.3% solids, and aftercentrifugation it contained 0.8% solids. 38.5% of the solids of thenigre were thus obtained as a bowl deposit in the centrifugal separator.

A sufficient quantity of cocoanut oil was next added to the nigreremaining in the kettle to effect neutral zation of all of the freealkali of the nigre. Stirring and heating were continued for an hourafter addition of the cocoanut oil, in order to insure neutralization ofall of the free nigre was neutralized with cocoanut oil fatty alkali.The resulting nigre was next passed through the centrifugal underconditions identical with the treatment of the unneutralized portion ofthe nigre which had previously been subjected to centrifugation. In thiscentrifugation, only 0.1% of solids remained in the centrifuged nigre.Approximately 92% of the content of solids was thus removed from theportion ofthe nigre neutralized with cocoanut oil.

Example II In an operation conducted in a manner analogous to that ofExample I, a sample of nigre containing 1.6% of solids was centrifugedwithout prior neutralization of alkali, with the result that the nigreeffluent from the centrifugal contained 0.9% solids, representing aremoval of 43.7% of the content of solids., In' a second operation,involving treatment of the same nigre after neutralization withhydrochloric acid, the nigre effluent from the centrifugal containedonly 0.1%

acids, and this second sample was then subjected to similarcentrifugation, with the result that the solids content was reduced to0.4%, representing an 87.1% removal of solids.

Example V A sample of nigre containing 2.2% solids was centrifugedwithout prior neutralization, and approximately 50% of the solidscontent was removed. in this operation. A second sample was neutralizedwith tallow acids, and the content of solids was reduced to 0.5%,representing a solids removal of 77.3%.

Example!!! A sample-of nigre containing 0.9% solids was centrifugedwithout pro-treatment, with. removal of approximately 50% of the solids.A similar samplewas then neutralized by treatment with cocoanut oil andcentrifuged, with the result that all but 0.01% of the solidswereremoved, repre- 'senting a 99% removal of solids.

Example VII A nigre sample containing 1.2% solids was neutralized withcocoanut oil fatty acids and centrifuged, with the result that thecontent of solids was reduced to 0.03%, representing a 97.5% removal ofsolids.

Still further modifications will be obvious to those skilled in the art,and we do not therefore wish to be limited except by the scope of thefollowing claims.

When reference is made in these claims to a source of acid thisexpression is used in the same sense as on pages 2 and 3 of thisspecifiof solids, representing removal of 93.7% of the content of solidsin the centrifugal.

Example III treated sample was reduced in solids content from 1.4% to0.8%, representing removal of 42.8% of the solids, while the neutralizedsample was reduced to 0.4% solids content, representing a 71.4% solidsremoval.

Example IV A sample of nigre containing 3.1% of solids was heated andcentrifugedas in Example I with out prior neutralization of the freealkali, with the result that approximately 50% of the solidswereremoved. A second sample of this same cation, to indicate either afree acid, or an ester capable of furnishing an acid radical forcombination with the free alkali of the nigre. When reference is made totreatment of the nigre with acid or reaction of the free alkali of thenigre with acid, treatments and reactions by which soap is formed by theaction of the free alkali upon any of theabove-mentioned sources of acidis included.

We claim:

1. In the separation of insoluble impurities from a soap nigrecontaining free alkali, the process comprising adding a source of acidto said nigre and reactingthe acid with the free alkali of the nigreuntil the quantity of said free alkali is substantially reduced, andthereafter removing insoluble impurities from the acid treated nigre,the reaction between the acid and nigre constituents being conducted insuch a manner as to avoid substantial splitting of the soap of thenigre. l

2. In the separation of insoluble impurities from a soap nigrecontaining free alkali, the process comprising adding a source of acidto said nigre and reacting the acid with the free alkali of the nigreuntil the quantity of said free alkali is substantially reduced, andthereafter removing insoluble impurities from the acid treated nigre bycentrifugation, the reaction between the acid and nigre constituentsbeing conducted in such a manner as to avoid substantial splitting ofthe soap of the nigre.

3. In the separation of insoluble impurities from a soap nigrecontaining free alkali, the process comprising adding a source of acidto saidnigre and reacting the acid with the free alkali of the nigreuntil the free alkali has been substantially completely neutralized, andtheretreated nigre, the reaction between the acid and nigre constituentsbeing conducted in such a manner as to avoid substantial splitting ofthe soap of the nigre.

4. In the separation of insoluble impurities from a soap nigrecontaining free alkali, the process comprising adding a source of acidto said nigre and reacting the acid with the free alkali of the nigreuntil the free alkali has been substantially completely neutralized, andthereafter removing insoluble impurities from the acid treated nigre bycentrifugation, the reaction between the acid and nigre constituentsbeing conducted in such a manner as to avoid substantial splitting ofthe soap of the nigre.

5. In the separation of insoluble impurities from a soap nigrecontaining free alkali, the process comprising adding a source oforganic acid to said nigre and reacting the acid withthe free alkali ofthe nigre until the quantity of said free alkali is substantiallyreduced, and thereafter removing insoluble impurities from the acidtreated nigre by centrifugation, the reaction between the acid and nigreconstituents being conducted in such a manner as to avoid substantialsplitting of the soap of the nigre.

'7. In the separation of insoluble impurities from a soap nigrecontaining free alkali, the

process comprising adding a source of a soap-.

forming organic acid to said nigre and reacting the acid with the freealkali of the nigre until the quantity of said free alkali issubstantially reduced, and thereafter removing insoluble impurities fromthe acid treated nigre.

8. In the separation of insoluble impurities from a soap nigrecontaining free alkali, the process comprising adding a source of asoapforming organic acid to said nigre and reacting the acid with thefree alkali of the nigre until the quantity of said free alkali issubstantially reduced, and thereafter removing insoluble impurities fromthe acid treated nigre by centrifugation.

9. In the separation of insoluble impurities from a soap nigrecontaining free alkali, the process comprising adding a source of ahigher aliphatic soap-forming acid to said nigre, and reacting the acidwith the free alkali of the nigre until the quantity of said free alkaliis substantially reduced, and thereafter removing insoluble impuritiesfrom the acid treated nigre.

10. In the separation of insoluble impurities from a soap nigrecontaining free alkali, the process comprising adding a source of ahigher aliphatic soap-forming acid to said nigre and reacting the acidwith the free alkali of the nigre until said free alkali issubstantially completely neutralized, and thereafter removing insolubleimpurities from the acid treated nigre.

11. In the separation of insoluble impurities from a soap nigrecontaining free alkali, the process comprising adding a source ofcocoanut oil acid to said nigre and reacting the acid with enema? afterremoving insoluble impurities from the acid the free alkali of the nigreuntil the quantity of said free alkali is substantially reduced, andthereafter removing insoluble impurities from the acid treated nigre.

12. In the separation of insoluble impurities from a soap nigrecontaining free alkali, the process comprising adding a source ofcocoanut oil acid to said nigre and reacting the acid with the freealkali of the nigre until the quantity of said free alkali issubstantially reduced, and thereafter removing insoluble impurities fromthe acid treated nigre by centrifugation.

,13. In the separation of insoluble impurities from a soapnigrecontaining free alkali, the process comprising adding a source ofcocoanut oil acid to said nigre and reacting the acid with the freealkali of the nigre until said free alkali is substantially completelyneutralized, and thereafter removing insoluble impurities from the acidtreated nigre by centrifugation.

14. In the manufacture of soap, the process comprising, saponifying asource of soap-forming acid, separating a nigre containing free alkalifrom the saponified mass, adding a source of acid to said nigre andreacting the acid with the free alkali of the nigre until the quantityof said free alkali is substantially reduced, thereafter removinginsoluble impurities from the acid treated nigre, and mixing thepurified nigre with other constituents in the manufacture of a furtherquantity of soap, the reaction between the acid .and nigre constituentsbeing conducted in such a manner as to avoid substantial splitting ofthe soap of the nigre.

15. In the manufacture of soap, the process comprising, saponifying asource of soap-forming acid, separating a nigre containing free alkalifrom the saponified mass, adding a source of acid to said nigre andreacting the acid with the free alkali of the nigre until the quantityof said free alkali is substantially reduced, thereafter removinginsoluble impurities from the acid treated nigre, and mixing thepurified nigre with a further quantity of a source of acid and of alkaliin the manufacture of a further quantity of soap, the reaction betweenthe acid and nigre constituents being conducted in such a manner as toavoid substantial splitting of the soap of the-nigre.

16. A process as defined in claim 14, in which the source of acid addedto the nigre is a source of cocoanut oil acids. 4

17. A process as defined in claim 14, in which the source of acid addedto the nigre is a source of higher fatty acids. 1

18. A process as defined in claim 14, in which the source of acid addedto the nigre is a source of soap-forming acid.

19. In the manufacture of soap, the process comprising, saponifying asource of soap-forming acid, separating a nigre containing free alkalifrom the saponified mass, adding a source of acid to said nigre andreacting the acid with the free alkali of the nigre until the quantityof said free alkali is substantially reduced, thereafter removinginsoluble impurities from the acid treated nigre by centrifugation, andmixing the purified nigre with other constituents in the manufacture ofa further quantity of soap, the reaction between the acid and nigreconstituents being conducted in such a manner as to avoid substantialsplitting of the soap of the nigre.

LEOPOLD SENDER. JAMES H. WILSON.

